Short-range communication technologies, such as Bluetooth and ZigBee, are intended to replace the cables connecting portable and/or fixed electronic devices. Key features of such technologies are robustness, low power consumption, and low cost.
However, due to their limited range of communication distance, low-power digital radio devices, such as Bluetooth and ZigBee devices, are not readily employed within larger scale environments (such as between multiple rooms in a building, or between multiple buildings) to transmit and control apparatus.
For example, Bluetooth is a wireless technology standard for exchanging data over short distances, designed for small-size personal devices such as mobile phones, tablets, and laptops. Target applications include networking of computers and peripherals, data transfer and synchronization, remote monitoring and control of smart appliances, heating systems, entertainment devices, and industrial automation. Bluetooth utilizes the unlicensed 2.4 GHz Industrial, Scientific, and Medical (ISM) band.
There are two forms of Bluetooth wireless technology systems: Basic Rate (BR) and Low Energy (LE). Both systems include device discovery, connection establishment and connection mechanisms. The BR system includes the optional Enhanced Data Rate (EDR) and Alternate MAC (Media Access Control)/PHY (Physical layer) (AMP) extensions. The LE system is designed for use with cases and applications with lower data rates and has lower duty cycles. LE systems usually have lower current consumption, lower complexity and lower cost than BR.
Bluetooth Low Energy (BLE) started as part of the Bluetooth 4.0 Core Specification. Although the Bluetooth specification covers both classic Bluetooth and Bluetooth Low Energy, these two wireless communication standards are not directly compatible and Bluetooth devices qualified on any specification version prior to 4.0 cannot communicate in any way with a BLE device. The on-air protocol, the upper protocol layers, and the applications are different and incompatible between the two technologies. However, dual-mode devices that implement both BR/EDR and BLE can communicate with any Bluetooth device.
In Classic Bluetooth, the BR/EDR radio operates in the unlicensed ISM band at 2.4 GHz. The system employs a frequency hopping transceiver to combat interference and fading. The basic hopping pattern is a pseudo-random ordering of the 79 designated Bluetooth channels, each having a bandwidth of 1 MHz. The hopping pattern can be adapted to exclude frequencies that are used by interfering devices. The slave devices in a piconet are synchronized to the common clock and frequency hopping pattern provided by the master device.
The physical channel is subdivided into 625 μs timeslots. Data is transmitted between Bluetooth devices in packets that are positioned in these slots. The master uses even-numbered slots to address each slave in turn, and each addressed slave has the opportunity to answer in the following odd-numbered timeslot. Frequency hopping takes place between the transmission or reception of packets.
The symbol rate is 1 megasymbol per second supporting the bit rate of 1 Megabit per second (Mbps) or, with EDR, a gross air bit rate of 2 or 3 Mbps. Bandwidth is required for a 72-bit access code to identify the piconet, and a 54-bit packet header to identify the slave. The radio also requires a guard band of at least 150 μs between packets to allow it to retune and stabilize on the next hopping frequency. Within a one slot packet, these requirements leave only a portion of the bandwidth for the payload data—and this can only be transmitted every other slot. One way to mitigate this limitation is to transmit for a longer period of time: 3 or 5 slots. All of the extra bandwidth can then be used for payload data. In a BR package, a five-slot packet can have up to 341 information bytes (including the 2-byte payload header) plus a 16-bit Cyclic Redundancy Check (CRC) code. A 32-bit Message Integrity Code (MIC) is also present when encryption is enabled.
Due to data being transmitted between Bluetooth devices in packets that are positioned in 625 μs timeslots with an Inter Frame Space of 150 μs between packets and the master using even-numbered slots to address a slave, and the slave answering in the following odd-numbered timeslot, real-time constraints can be a problem if Bluetooth devices are not configured to operate in the normal way. Similarly, ZigBee is a standard specification that relates to technology that is designed to be of low cost and low complexity, with devices having a limited range of transmission.